A Method to measure +/ detection efficiency asymmetry at LHCb
Liming Zhang
08/15/07
2
Idea
• Partially reconstruct D+ sD0, D0KS
0+without => partial yield
• Combine to fully reconstruct D0 => full yield • full/partial yield => absolute efficiency
• Br(bD*+X) = (17.3 2.0)%
• Br(D*+ D0 KS0(++ ) = (1.36 0.09)%
3
MC Samples
• 491 k signal MC B0D*+, D*to this channel• 680 k inclusive b MC• 766 k inclusive b biased MC
4
Signal MC
M(KS +)
m = M(KS ++) M(KS +)
M(KS +) in [1.5, 1.7] GeV
M(KS +) in [1.0, 1.3] GeV
Reconstructed Distributions
Only consider this region here
5
Optimization of Selection Criteria
• Maximize Figure of Merit FOM = S/sqrt(S+B) on inclusive b MC
• S: signal yield in this inclusive b MC, predicted by using efficiency from signal MC
• B: background yield scaled from m sideband of this inclusive b MC
• The signal region: m<15 MeV
• Sideband region: [50, 150] MeV
m background distribution
Sideband region
Signal
region
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KS0 reconstruction
• KSDD (2/3) (only used here) • KSLL (1/3)
• Daughters IP significance > 2• Daughters track fit • Vertex • Pt > 1 GeV/c• Proper time/life time > 0.17• Vr>21 mm• Vz [150, 2330] mm
• Mass window 17 MeV
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Distributions of KS0
purity 80% ~ 10 MeV
0
000
)(S
SS
Kz
Dz
Kz
K
P
VVmt
> 21 mm
>0.17
[150,2330] mm
17 MeV
Signal
Background
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Selection Criteria
• Prompt + from D0:– PID
– IP significance > 5
– Pt > 700 MeV
Signal
Background
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Selection Criteria
• slows+:
– IP significance > 1
– Pt > 220 MeV
Signal
Background
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Selection Criteria
• D0 vertex • D* vertex • Multiply candidates selection
– Same D0 combines with several slow pion
– Choose the one which has the best D* vertex
– B/S reduced from 2.0 to 1.7
• Not helpful from cuts on IP significance, flight distance (significance) etc.
11
Results of partial reconstruction
• Efficiency (before Trigger) = NREC/NGEN GEN = 1656/391k 20% = (0.85 0.02) 103
• Annual yield (before Trigger)– S = 2fb1500b2(17.32.0)%(1.360.09)%(0.85 0.02)
103
= (4.0 0.3) 106
• Signal from bb inclusive MC data– Expect 31
– 29 found
– Fit gives 339
– B/N ~ 1.7
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TO DO
• To check background sources and further suppress background level if possible
• Trigger efficiency
• To fully reconstruct D0 by combining with partially reconstructed candidate
• To find efficiency of and give the prediction of stat. error on detection asymmetry from this method